Conventionally, in a horizontal DMOS (Double-Diffused Metal-Oxide-semiconductor Field Effect Transistor) the drain layer has been separated into a drift layer that mainly passes a current and a drain buffer layer that mainly ensures a breakdown voltage. Since they have been controlled separately, it has been difficult to achieve both an increase in breakdown voltage and an improvement in current performance per unit area. In the case where only the drift layer is provided and the drain buffer layer is not provided, it has been difficult to improve the breakdown voltage; and in the case where the necessary breakdown voltage is ensured, the element area has tended to be increased.